The rare gases, krypton and xenon, are finding increasing application in industrial and other uses. Krypton is being widely used in high quality lighting including long-life light bulbs and automotive lamps. Xenon is being used for medical applications, including special x-ray equipment. Both gases are commonly used in many laboratory and research applications. The source of krypton and xenon is the atmospheric air which contains 1.14 ppm krypton and 0.087 ppm xenon for a krypton to xenon ratio of 13:1. During air separation processes that involve the cryogenic separation of the air, the krypton-xenon tends to concentrate with the oxygen product. Accordingly, the primary source of krypton-xenon is from air separation plants and involves further processing of the oxygen product to recover the krypton-xenon content. Examples of recent advances in such krypton-xenon recovery processes may be found in U.S. Pat. No. 4,401,448--La Clair, U.S. Pat. No. 4,568,528--Cheung and U.S. Pat. No. 4,574,006--Cheung.
Because most of the krypton and xenon in the air is recovered and further processed, the krypton product to xenon product ratio is about the same as their composition ratio in the atmospheric air, i.e. about 13:1. However, the demand for xenon is presently increasing at a faster rate than that for krypton primarily because of the rate of xenon application in the medical field. Xenon is a major portion of the fill gas in detectors used with computerized axial tomography (CAT) scanners and is also used as part of a breathing mixture for patients undergoing a CAT scan. Accordingly it is desirable to lower the krypton-xenon ratio of the recovered rare gases by enhancing the production of xenon produced by cryogenic rectification.
It is an object of this invention to provide a method for enhancing the production of xenon produced by cryogenic rectification of a mixture containing krypton and xenon.
It is another object of this invention to provide apparatus useful for enhancing the production of xenon produced by cryogenic rectification of a mixture containing krypton and xenon.